Tube arrangement for frequency doubling



' Aug. 5, 1947.

Filed Sept. 21, 1940' 3 M 5 1 T 5 m. in W "1 g E a 0 i J w vl v 55 3 5 5 A EW r p F in v a (a m n F 7,0,.

ATTORNEY PHASE saw-7n? Patented Aug. 5, 1947 TUBE ARRANGEMENT FOR FREQUENCY DOUBLING Andrew Alford, New York, N. Y., assignor to Federal Telephone andRadio Corporation, a corporation of Delaware ATENT OFFIC',

Appiication September 21, 1941), Serial No. 357,764.

4 Claims.

This invention relates to frequency doubling devices, and more particularly to electron tube arrangements operating on the principle of velocity modulation for producing frequency multiplication.

In a known form of circuit a beam or stream of electrons is modified in velocity at a given point. The electrons of the beam are then permitted to form into bunches or groups due to the change in velocity by traveling at given distance. By properly choosing this drift distance the electrons reach a point of maximum bunching or grouping. A resonant circuit is coupled to extract the energy from the bunched electrons. This resonant circuit is tuned to the fundamental frequency which corresponds substantially with the grouping of the electron bunches.

According to one feature of my invention I provide a tubecircuit with a velocity modulating circuit similar to those of the prior art for modulating the beam at a given fundamental frequency. However, instead of providing a second resonant circuit at the optimum spacing for operation at the fundamental frequency, I provide a drift distance greater than this spacing so that the electrons within the bunches tend to spread, because of the combined effect of velocity differences and the inter-electron repulsion. Consequently the bunchings and rarefractions are no longer substantially symmetrical, since the additional effect of electron repulsion tends to spread the bunches to an extent greater than the increase in density of the electrons in the rarefied portions of the beam. Consequently, the wave form is such as to be rich in even harmonics. I then provide a tuned circuit to an even harmonic, preferably the second, to extract energy from the beam.

It is a principal object of my invention to utilize the inherent distribution of electrons in a velocity modulated beam after passing the optimum drift distance to produce a harmonic oscillation,

Although the waves produced when the bunches are permitted to pass the optimum bunching position are rich in even harmonics, a considerable portion of the energy still is at the fundamental frequency. Unless this energy can be made to do useful work it will have to be dissipated in the form of heat or other wasteful 2 forms and the circuit will consequently be of rather low emciency.

In accordance withanother feature of my invention I provide means for utilizing part of this otherwise wasted energy and so increase the effi ciency of the system. One manner of accomplishing this consists in providing a resonant circuit tuned to the fundamental frequency for extracting energy from the beam after it passes the harmonic resonant circuit, and feeding back regeneratively from this latter circuit to the other tube input circuit.

A better understanding of my invention, and the objects and features thereof will be had from the particular description thereof made with reference to the accompanying drawing in which Fig. 1 is a diagrammatic showing for the purpose of explaining my invention;

Fig. 1A shows distribution curves to explain the operation of my invention, and

Fig. 2 shows in section a preferred structural embodiment of my invention.

In Fig. 1 is diagrammatically shown a circuit arrangement for illustrating the operation of. my invention. An emissive cathode Illemits a group of electrons which are formed into a beam by accelerating electrode I I or other means. The electrons formed in this beam are then passed through a pair of grids l3, M, which may be arranged in an oscillating circuit l5, Oscillating circuit I5 is diagrammatically shown as a closed circuit. It is clear that any suitable tuned circuit may be used, preferably a completely closed tuned circuit is provided in order to reduce losses to a minimum. Energy for a fundamental frequency is fed into circuit 15 over a transmission line It and circuit 15 is tuned to this fundamental frequency. 'As the electron beam passes between grids l3, l4, a change in velocity is caused in certain of the electrons, the beam depending upon the instantaneous potential of the grids. The electronbeam is then allowed to traverse a certain distance.

After reaching a position such as a, the electrons, due to the change in velocity caused by the control grids l3, I4, will become concentrated so that their distribution produces a Wave form which may be illustrated as a sinusoidal wave 38, Fig. 1A. The electron beam is then allowed to traverse a further distance to tuned circuit l1.

3 In traversing this additional distance the electrons in the bunched group tend to become redistributed due to their velocity differences and further, because of interelectron repulsion. However, in the spaces between the bunches where the electrons have become more widely spaced, which is represented by the negative portion of curve 30, the change in distribution after traversing this shorter distance from A to I! i not the same as that for the more densely bunched electrons, because of the absence of electron repulsion. Accordingly, traversing this distance, the electron distribution is changed so as to correspond more nearly to curve 3! of Fig. 1A. It can be seen from the unsymmetrical form of this curve that the electron stream as now con-.

Accordingly,

If nothing more is provided in the system the second harmonic energy may be still extracted. However, the efficiency of the system will be relatively low, ince considerable energy of other frequencies still is possessed by the electron beam. Accordingly, in order'to enhance the efiiciency of the system, I permit the electron beam to traverse a further distance to tuned circuit .32 which is tuned to the fundamental frequency. Preferably,'the spacing between Hand 32 is such as to allow a maximum grouping of the electrons again at the fundamental frequency. The energy is then extracted from the beamby means of grids 22, 23 of tuned circuit 32,and if desired the electrons after passing through these grids may be collected on a target'electrode 2 S so as to remove them from the system. .An output line 25 is coupled to circuit 32 and the fundamental frequency energy from 32 is fed back over a line 26 anda suitable phase adjustor 21 to input line 16. .Accordingly, the energy .extracted by circuit 32 serves to furnish energy in regenerative relation to the input of circuit 15. Accordingly, the e ciency of the multiplier is greatlyenhanced.

It is clear that this circuit-is only diagrammatically illustrated and that many various -practicalformsumay be'provided. The precise form of :the resonant'circuits .15, ill and 32 is not important, since my invention will operate to'produce the desired .results so long as anysuitable tuned circuits :are provided. It is preferable. however in order to maintain the losses of the system at a low value, to utilize low loss resonant circuits.

One practical embodiment of my invention is disclosed in" Fig. 2 wherein similar reference characters are used to indicate the tube elements corresponding to those5shown in Fig. 1. In this figure, cathode l0 and accelerating electrode H are arranged in .a chamber which is closed by means of a glass seal 40. The electrons emitted by cathode H are guided bymeans of tube '4! into a resonant chamber i5 wherein they are changed in velocityby'rneans of'grids l3, it. The electrons passingfrom grid M are then permitted to drift in a tube 42 which serves to prevent any extraneous influence on the electronbeamsafter leaving grid [4. Electron streams then pass between grids l8,2| and resonant chamber ll which is tuned to an even harmonic, such as the second harmonic. A concentric line 21 is coupled to circuit 1'! for extracting the harmonic energy therefrom. After leaving grid 29 the-electrons 4 again pass through a tube 43 to grids 22, 23, associated with a tuned resonant chamber 32 and from there the electron stream passes through a tube 44 to a sealed chamber 45 where they are collected by electrode 24. A concentric line 25 is provided for extracting energy from tuned circuit 32 and this energy is fed back over line 25 through phase shifter 27 to the input line i 6 into chamber l5. Line 16 is preferably also a concentric conductor line so as to provide eflicient transmission of the high frequency input energy.

It is clear that the arrangement of Fig. 2 provides a very low loss circuit, since all of the tuned circuits connected therewith are complete closed chambers which produce very little attenuation. Furthermore, .by providing the concentric lines 'agood shielding conductor arrangement for the high frequency energy is provided. 'Ittis clear that Fig. 2 illustrates merely a preferred embodiment of my invention and should not be considered as a limitation thereon. Many other methods of achieving the results set forth in the present application may be provided by those skilled in the art. What I consider to be my invention and desire to protect by Letters Patent is embodied in the accompanying claims.

What I claim is:

1. A frequency multiplier comprising means for producing a beam of electrons-moving ata given velocity, means for modifying the velocity of electrons in said beam in accordance with a fundamental frequency, means tuned to an even harmonic of said'fundamental frequency for extracting energy at saidharmonicfrequency from said beam of electrons so modified in velocity, means tuned to said fundamental frequency for extracting fundamental frequency from said beam, means transferring electrons leaving said means tuned to a harmonic frequency to said means tuned at fundamental frequency, and means for feeding energy from said second tuned means to said velocity modifyingmeans.

2. A frequency multipliercomprisingmeansfor producing a beam of electrons moving at a given velocity, means for modifying'the velocity of the electrons in accordance with a fundamental frequency, means tuned to an even harmonic of said fundamental frequency for extracting energy from said beam at the derived position of electron distribution of high even harmonic content, means tunedto said fundamental frequency for extracting fundamental frequency energy from said beam after passing said harmonic tuned means, and means for feeding said extracted fundamental frequency energy to said velocity modifying means in regenerative phase.

3. The method of frequency multiplicationcomprising forming a beam "of electrons moving at a given'velocity, modifying the velocity of electrons in said beam in accordance with a fundamental frequency, passing-the electrons in said beam until they become bunched'into *a-wave form rich in even harmonics by'combined action of said velocity modulation and the inherent electron repulsion, extracting from said beam energy at a harmonic frequency, thereafterpassing the-electrons until they become bunched into a wave form rich in said fundamental-frequency, extracting energyfrom said beam at said fundamental frequency,-and"feeding back said last-extracted energy ,furtherto-modify the velocity of electrons insaidbeam i r v 4. A high frequency multiplier comprising means for producing-a beam 'of electrons mov ing at a given-velocity, means for modifying'the 5 6 velocity of electrons in said beam in accordance with a fundamental frequency, means for .per- FEFERENCES QITED mitting said electrons to become partially dis- The following references are of record in the tributed in relation to the maximum .bunched file Of this p t group in order to produce a position along said- 5 beam rich in even harmonics, means tuned to an UNITED STATES PATENTS even harmonic of said fundamental frequency for Number Name Date extracting energy of said harmonic frequency at 2,222,399 Frainc el Nov. 26, 1940 the said position, followed by means tuned to said 2,305,883 Litton Dec. 22, 1942 fundamental frequency for extracting funda- 10 7 ,193 Fisk Mar. 27, 1945 mental frequency energy from said beam, 2,280,824 Hansen Apr. 28, 1942 ANDREW ALFORD. 2,281,935 Hansen May 5, 1942 

